1. Field of the Invention
The present invention relates generally to an extrusion process and apparatus therefor, and more particularly to a hydrostatic extrusion process and apparatus therefor whereby the time period for an extrusion cycle may be shortened and damage to the extrusion mandrel, when used to extrude tubular members, may be prevented.
2. Description of the Prior Art
A hydrostatic extrusion process is well known as the most efficient plastic working process since it provides a high lubricity between the billet and the extrusion die thereby facilitating extrusion at a high extrusion ratio. Within conventional hydrostatic extrusion processes, however, the pressure medium is frequently recovered each time an extrusion is completed, and several steps, such as, for example, charging a billet into the container and supplying the pressure medium thereinto, and the like, are required to be performed before performance of the extrusion operation. Consequently, it is difficult to perform an extrusion of a material in a continuous manner, and therefore, efficient workability of the hydrostatic extrusion cannot be reflected in substantial productivity.
Within a known hydrostatic extrusion press of the type which performs extrusion of hollow material, a mandrel holding fixture is fixedly connected to columns which are caused to extend, due to the compression load applied to the mandrel during the extrusion, and to contract when the extrusion pressure is released, whereby the mandrel is subjected to such extreme compression loads and is consequently damaged thereby. Another problem inherent in this type of prior art resides in the fact that it is difficult to initially provide complete sealing between a hollow billet and the mandrel and to simultaneously be able to move the mandrel to a suitable position at which the extrusion starting pressure may be applied.